Note: the actual testing of stems is
over with, but please feel free to criticize or make
suggestions about this page. Contact Damon Rinard: drinard@yahoo.com

The crew at Bill Holland Cycles
performed some stem fatigue testing in 1995 or so. Bill
Holland kindly gave permission for me to post the results
here. On this page I'll try to describe the test protocol and
other interesting bits about the testing.

Test Protocol

Setup

The fixture used was a rigid square
steel structure with a fork steerer tube welded vertically
into it. For testing, each stem was mounted in the fixture's
steerer tube using its own expander bolt and wedge just as it
would be installed in a real fork. All stems were mounted at
the indicated maximum height line.

Static Loading

A technician bolted a long steel bar
into the stem like a straight handlebar. Weights were added
to one end of the bar until a torque load of 1651 in*lbf was
on the stem. Downward deflection was measured parallel to the
stem's quill at a point on the bar 5 inches from the
centerline of the stem.

Fatigue loading

Loading during fatigue testing for all
stems was +1651, -0 in.lb. at approximately 1 cycle per
second, applied to just one side of the stem.

Feel free to contact me, Damon Rinard,
at drinard@yahoo.com
for clarification on testing methods, etc., but please
contact Holland Cycles
directly to get a brochure or place an order:

Raw Data

In the chart below,

STEM is the stem
tested.CYCLES is the number of load cycles to
fatigue failure.WEIGHT is the mass of the stem in grams.DEFLECTION is how far, in inches, the bar
moved with the 1651 in*lbf torque load applied.ST/WT is the stiffness-to-weight ratio of
each stem. It is 1000*(1/DEFLECTION)/WEIGHT, in 1000/(in*g).

A Cinelli XA was initially included in
the test, but twice during fatigue testing the stem binder
bolt broke. The stem itself didn't show any kind of failure,
so after replacing the bolt the test continued to failure.
Later the standard loading for fatigue testing was changed,
so the data for this stem is not comparable to the others.

The 3TTT Synthesis failed during the
night when the expander bolt's head broke off. However, the
cone did not come loose and the test continued without the
expander bolt until the deflection increased dramatically. We
stopped the test and removed the stem, and only then
discovered a crack growing from the corner of one of the
slots in the quill hidden deep inside the steerer.

Most of the other failures were cracks
in the quill tube, extension tube or the weld connecting
these two tubes. Here's a sampling of the notes on failure
modes:

Cracked in quill at bottom weld.
Cracked in extension at quill.
Welds polished around quill. Did not break.
Cracked in quill, across weld.
Cracked in quill, across weld.
Quill cracked below bottom weld.
Cracked along top of extension and on the compression side of quill weld.
Cracked in quill, across weld.
Cracked in extension at handlebar clamp. Across weld.